workqueue: Restrict affinity change to rescuer

[ Upstream commit 640f17c82460e9724fd256f0a1f5d99e7ff0bda4 ]

create_worker() will already set the right affinity using
kthread_bind_mask(), this means only the rescuer will need to change
it's affinity.

Howveer, while in cpu-hot-unplug a regular task is not allowed to run
on online&&!active as it would be pushed away quite agressively. We
need KTHREAD_IS_PER_CPU to survive in that environment.

Therefore set the affinity after getting that magic flag.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210121103506.826629830@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 0695c7895c892d4f2498111df6c4e929e6b3752e..1d99c52cc99a6ce9c0639b3f7a5bcf44ab8b6473 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1845,12 +1845,6 @@ static void worker_attach_to_pool(struct worker *worker,
 {
        mutex_lock(&wq_pool_attach_mutex);
 
-       /*
-        * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
-        * online CPUs.  It'll be re-applied when any of the CPUs come up.
-        */
-       set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
-
        /*
         * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains
         * stable across this function.  See the comments above the flag
@@ -1859,6 +1853,9 @@ static void worker_attach_to_pool(struct worker *worker,
        if (pool->flags & POOL_DISASSOCIATED)
                worker->flags |= WORKER_UNBOUND;
 
+       if (worker->rescue_wq)
+               set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
+
        list_add_tail(&worker->node, &pool->workers);
        worker->pool = pool;